Hard amorphous carbon film containing ultratrace hydrogen for magnetic recording media and magnetic heads

ABSTRACT

A magnetic recording medium according to one embodiment includes at least a ground layer above a non-magnetic substrate; a magnetic recording layer above the ground layer; and an overcoat above the magnetic recording layer, the overcoat characterized in that said overcoat is an amorphous carbon film having a ratio of sp 3  bonding with respect to sp 2  bonding (sp 3 /(sp 2 +sp 3 )) of at least 0.5, and hydrogen content in the overcoat in a center layer thereof in a film thickness direction of said overcoat is from 0.1 atom % to 0.6 atom %. Additional products and methods are also presented.

FIELD OF THE INVENTION

The present invention relates to data storage systems, and moreparticularly, this invention relates to various components of magneticstorage systems having a superhard amorphous carbon film thereon, andmethods of forming the same.

BACKGROUND

The heart of a computer is a magnetic hard disk drive (HDD) whichtypically includes a rotating magnetic disk, a slider that has read andwrite heads, a suspension arm above the rotating disk and an actuatorarm that swings the suspension arm to place the read and/or write headsover selected circular tracks on the rotating disk. The suspension armbiases the slider into contact with the surface of the disk when thedisk is not rotating but, when the disk rotates, air is swirled by therotating disk adjacent an air bearing surface (ABS) of the slidercausing the slider to ride on an air bearing a slight distance from thesurface of the rotating disk. When the slider rides on the air bearingthe write and read heads are employed for writing magnetic impressionsto and reading magnetic signal fields from the rotating disk. The readand write heads are connected to processing circuitry that operatesaccording to a computer program to implement the writing and readingfunctions.

The volume of information processing in the information age isincreasing rapidly. In particular, HDDs have been desired to store moreinformation in its limited area and volume. A technical approach to thisdesire is to increase the capacity by increasing the recording densityof the HDD. To achieve higher recording density, further miniaturizationof recording bits is effective, which in turn typically requires thedesign of smaller and smaller components.

The further miniaturization of the various components, however, presentsits own set of challenges and obstacles.

As described above, a magnetic disk drive uses a magnetic head to recordand play back the information on a magnetic disk (magnetic recordingmedium). As the magnetic spacing becomes smaller, the magnetic head andthe magnetic disk can be closer, and information can be recorded inmicroscopic regions, and the minute magnetic signals on the magneticdisk can be played back. When the head-disk spacing narrows, the filmthicknesses of the overcoats of the magnetic disk and the magnetic headmust be reduced.

However, in order to prevent corrosion of the metals used in therecording layer of the magnetic disk and the recording and playbackelement of the magnetic head, the overcoat must be chemically stable,dense, and uniform. In addition, when the magnetic head is extremelyclose to the magnetic disk, sufficiently high resistance to abrasionmust be present because of the relative rotational motions. Moreover,generally, as conventional overcoats of the magnetic disk and themagnetic head become thinner, the corrosion resistance degrades becausethe coverage decreases; the effective hardness decreases; and theabrasion resistance degrades. Therefore, in order to achieve thinnerovercoats for the magnetic disk and the magnetic head while maintainingcorrosion resistance and abrasion resistance, the density and hardnessof the overcoats of the magnetic disk and the magnetic head must beimproved, and the degradation caused by the thinner film thickness mustbe corrected.

In order to improve the recording density, suppression of thermaldemagnetization of the recording medium and maintenance of the writecharacteristics should be simultaneously satisfied. The bit diameter ofthe recording medium should also be on the order of nanobits in order toachieve a high recording density. However, the problem of thermaldemagnetization arises as the bit diameter decreases.

Information recorded on the recording medium is lost as time elapsesbecause of fluctuations in the thermal magnetization, which causethermal demagnetization. To solve the problem of thermaldemagnetization, the thermal stability of the magnetization may beimproved by using a material having high magnetic anisotropy. However,when the magnetic anisotropy becomes too high, the magnetization of therecording medium cannot be reversed by the recording magnetic field fromthe magnetic head recording element, and consequently, the magneticmedium is no longer able to be written to.

Specifically, to improve the surface recording density, new technologiesare indispensable to simultaneously achieve the suppression of thermaldemagnetization and the maintenance of the writing characteristics tothe recording medium. One proposed method for solving this problem isthermally assisted recording (TAR). In this technology, magneticrecording is conducted while the coercive force is decreased bytemporarily and locally heating the recording medium. By using thistechnology, writing is possible even for a recording medium having highmagnetic anisotropy. As a result, the suppression of thermaldemagnetization and the maintenance of the characteristics of writing tothe recording medium are satisfied simultaneously, and a dramaticincrease in the surface recording density can be realized. Consequently,thermal resistance becomes necessary for the overcoats of the magneticdisk and the magnetic head.

In particular, the development of technologies for improving the thermalresistance of the head-disk interface (HDI) is essential in producing apractical TAR method. A conventional HDI is composed of a magnetic headovercoat, a magnetic disk overcoat, and a lubricant film, each of whichplays a role in preventing corrosion and abrasion of the head and disk,and maintaining high reliability of the magnetic disk drive. However,the structural elements of the HDI have carbon as the primary componentand are believed to be susceptible to heat compared to metals orceramics. Therefore, in the high temperature environment of TAR, the HDIstructural elements are typically deformed and/or degraded by heat. As aresult, degradation and deformation are concerns in the reliability ofthe magnetic recording system.

Conventional diamond-like carbon (DLC) films have been used as the diskovercoats of the HDI structural elements. However, in a high temperatureenvironment considering the application to TAR, the mechanicalresistance and chemical resistance required as the distance between thehead and disk narrows must also be thermally stable for desirableresults. Therefore, a property of the desired DLC film is an overcoathaving high film density, that is, enhanced sp³ bonding (e.g., a diamondstructure).

However, DLC films produced by a conventional sputtering method have astructure close to that of graphite, thereby having few sp³ bonds.Moreover, a DLC film formed by chemical vapor deposition (CVD) includeshydrogen in the film because a hydrocarbon gas is used as a rawmaterial, but it is difficult to achieve a high sp³ bonding ratio viathis method.

As described above, in order to achieve a higher recording density inmagnetic disk drives, the demands for the overcoats of the magnetic diskand the magnetic head are a thinner shape and higher thermal resistance.To ensure higher reliability as a magnetic disk drive, higher density,hardness, and higher thermal resistance are desirable.

Thus it would be beneficial to develop a system with high recordingdensity by improving the corrosion resistance and abrasion resistance inorder to produce thinner films. Moreover it may be beneficial to improvethe heat resistance in order to improve the practicality of implementingTAR.

SUMMARY

A magnetic recording medium according to one embodiment includes atleast a ground layer above a non-magnetic substrate; a magneticrecording layer above the ground layer; and an overcoat above themagnetic recording layer, the overcoat characterized in that saidovercoat is an amorphous carbon film having a ratio of sp³ bonding withrespect to sp² bonding (sp³/(sp²+sp³)) of at least 0.5, and hydrogencontent in the overcoat in a center layer thereof in a film thicknessdirection of said overcoat is from 0.1 atom % to 0.6 atom %.

A magnetic head according to another embodiment includes a playbackelement; and an overcoat above a media-facing side of the playbackelement, the overcoat characterized in that said overcoat is anamorphous carbon film having a ratio of sp³ bonding with respect to sp²bonding (sp³/(sp²+sp³)) of at least 0.5, and hydrogen content in thefilm in a center layer in a film thickness direction of said overcoat isfrom 0.1 atom % to 0.6 atom %.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a disk drive system, which may include a magnetic head, adrive mechanism for passing a magnetic medium (e.g., hard disk) over themagnetic head, and a controller electrically coupled to the magnetichead.

A method according to yet another embodiment includes forming anovercoat above at least one of a magnetic layer of a magnetic medium anda media-facing side of the playback element, the overcoat characterizedin that said overcoat is an amorphous carbon film having a ratio of sp³bonding with respect to sp² (sp³/(sp²+sp³)) bonding of at least 0.5, andhydrogen content in the film in a center layer in a film thicknessdirection of said overcoat is in a range of from 0.1 atom % to 0.6 atom%, wherein the hydrogen content of said overcoat is adjusted to be insaid range by adjusting a flow of hydrogen gas into a film depositionchamber during deposition of the overcoat, and by adjusting a hydrogengas pressure in said film deposition chamber.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 is a simplified drawing of a magnetic recording disk drivesystem.

FIG. 2A is a schematic representation in section of a recording mediumutilizing a longitudinal recording format.

FIG. 2B is a schematic representation of a conventional magneticrecording head and recording medium combination for longitudinalrecording as in FIG. 2A.

FIG. 2C is a magnetic recording medium utilizing a perpendicularrecording format.

FIG. 2D is a schematic representation of a recording head and recordingmedium combination for perpendicular recording on one side.

FIG. 2E is a schematic representation of a recording apparatus adaptedfor recording separately on both sides of the medium.

FIG. 3A is a cross-sectional view of one particular embodiment of aperpendicular magnetic head with helical coils.

FIG. 3B is a cross-sectional view of one particular embodiment of apiggyback magnetic head with helical coils.

FIG. 4A is a cross-sectional view of one particular embodiment of aperpendicular magnetic head with looped coils.

FIG. 4B is a cross-sectional view of one particular embodiment of apiggyback magnetic head with looped coils.

FIG. 5 is a partial cross-sectional view of a magnetic recording mediumaccording to one embodiment.

FIG. 6 is a process flowchart for a method according to one embodiment.

FIG. 7 is a graph showing the measurement results of the film densitywith respect to the hydrogen content in the film according to oneembodiment.

FIG. 8 is a graph showing the measurement results of the film hardnesswith respect to the hydrogen content in the film according to oneembodiment.

FIG. 9 is a graph showing the measurement results of the residual filmthickness of the carbon film with respect to the heating time accordingto one embodiment.

FIG. 10 is a graph showing the measurement results of the hydrogencontent of a superhard amorphous carbon film according to oneembodiment.

FIG. 11A is a graph showing the measurement results of the hydrogencontent of several superhard amorphous films according to oneembodiment.

FIG. 11B is a detailed view of the graph in FIG. 11A, showing themeasurement results of the hydrogen content of superhard amorphouscarbon film according to one embodiment.

FIG. 12 is a schematic diagram of a vapor deposition tool using arcdischarge according to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofdisk-based storage systems and/or related systems and methods, as wellas operation and/or component parts thereof.

In one general embodiment, a magnetic recording medium includes at leasta ground layer above a non-magnetic substrate; a magnetic recordinglayer above the ground layer; and an overcoat above the magneticrecording layer, the overcoat characterized in that said overcoat is anamorphous carbon film having a ratio of sp³ bonding with respect to sp²bonding (sp³/(sp²+sp³)) of at least 0.5, and hydrogen content in theovercoat in a center layer thereof in a film thickness direction of saidovercoat is from 0.1 atom % to 0.6 atom %.

In another general embodiment, a magnetic head includes a playbackelement; and an overcoat above a media-facing side of the playbackelement, the overcoat characterized in that said overcoat is anamorphous carbon film having a ratio of sp³ bonding with respect to sp²bonding (sp³/(sp²+sp³)) of at least 0.5, and hydrogen content in thefilm in a center layer in a film thickness direction of said overcoat isfrom 0.1 atom % to 0.6 atom %.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a disk drive system, which may include a magnetic head, adrive mechanism for passing a magnetic medium (e.g., hard disk) over themagnetic head, and a controller electrically coupled to the magnetichead.

In one general embodiment, a method includes forming an overcoat aboveat least one of a magnetic layer of a magnetic medium and a media-facingside of the playback element, the overcoat characterized in that saidovercoat is an amorphous carbon film having a ratio of sp³ bonding withrespect to sp² (sp³/(sp²+sp³)) bonding of at least 0.5, and hydrogencontent in the film in a center layer in a film thickness direction ofsaid overcoat is in a range of from 0.1 atom % to 0.6 atom %, whereinthe hydrogen content of said overcoat is adjusted to be in said range byadjusting a flow of hydrogen gas into a film deposition chamber duringdeposition of the overcoat, and by adjusting a hydrogen gas pressure insaid film deposition chamber.

Referring now to FIG. 1, there is shown a disk drive 100 in accordancewith one embodiment of the present invention. As shown in FIG. 1, atleast one rotatable magnetic disk 112 is supported on a spindle 114 androtated by a drive mechanism which may include a disk drive motor 118.The magnetic recording on each disk is typically in the form of anannular pattern of concentric data tracks (not shown) on the disk 112.

At least one slider 113 is positioned near the disk 112, each slider 113supporting one or more magnetic read/write heads 121. As the diskrotates, slider 113 is moved radially in and out over disk surface 122so that heads 121 may access different tracks of the disk where desireddata are recorded and/or to be written. Each slider 113 is attached toan actuator arm 119 by means of a suspension 115. The suspension 115provides a slight spring force which biases slider 113 against the disksurface 122. Each actuator arm 119 is attached to an actuator 127. Theactuator 127 as shown in FIG. 1 may be a voice coil motor (VCM). The VCMcomprises a coil movable within a fixed magnetic field, the directionand speed of the coil movements being controlled by the motor currentsignals supplied by controller 129.

During operation of the disk storage system, the rotation of disk 112generates an air bearing between slider 113 and disk surface 122 whichexerts an upward force or lift on the slider. The air bearing thuscounter-balances the slight spring force of suspension 115 and supportsslider 113 off and slightly above the disk surface by a small,substantially constant spacing during normal operation. Note that insome embodiments, the slider 113 may slide along the disk surface 122.

The various components of the disk storage system are controlled inoperation by control signals generated by controller 129, such as accesscontrol signals and internal clock signals. Typically, control unit 129comprises logic control circuits, storage (e.g., memory), and amicroprocessor. The control unit 129 generates control signals tocontrol various system operations such as drive motor control signals online 123 and head position and seek control signals on line 128. Thecontrol signals on line 128 provide the desired current profiles tooptimally move and position slider 113 to the desired data track on disk112. Read and write signals are communicated to and from read/writeheads 121 by way of recording channel 125.

The above description of a typical magnetic disk storage system, and theaccompanying illustration of FIG. 1 is for representation purposes only.It should be apparent that disk storage systems may contain a largenumber of disks and actuators, and each actuator may support a number ofsliders.

An interface may also be provided for communication between the diskdrive and a host (integral or external) to send and receive the data andfor controlling the operation of the disk drive and communicating thestatus of the disk drive to the host, all as will be understood by thoseof skill in the art.

In a typical head, an inductive write head includes a coil layerembedded in one or more insulation layers (insulation stack), theinsulation stack being located between first and second pole piecelayers. A gap is formed between the first and second pole piece layersby a gap layer at an air bearing surface (ABS) of the write head. Thepole piece layers may be connected at a back gap. Currents are conductedthrough the coil layer, which produce magnetic fields in the polepieces. The magnetic fields fringe across the gap at the ABS for thepurpose of writing bits of magnetic field information in tracks onmoving media, such as in circular tracks on a rotating magnetic disk.

The second pole piece layer has a pole tip portion which extends fromthe ABS to a flare point and a yoke portion which extends from the flarepoint to the back gap. The flare point is where the second pole piecebegins to widen (flare) to form the yoke. The placement of the flarepoint directly affects the magnitude of the magnetic field produced towrite information on the recording medium.

FIG. 2A illustrates, schematically, a conventional recording medium suchas used with magnetic disc recording systems, such as that shown inFIG. 1. This medium is utilized for recording magnetic impulses in orparallel to the plane of the medium itself. The recording medium, arecording disc in this instance, comprises basically a supportingsubstrate 200 of a suitable non-magnetic material such as glass, with anoverlying coating 202 of a suitable and conventional magnetic layer.

FIG. 2B shows the operative relationship between a conventionalrecording/playback head 204, which may preferably be a thin film head,and a conventional recording medium, such as that of FIG. 2A.

FIG. 2C illustrates, schematically, the orientation of magnetic impulsessubstantially perpendicular to the surface of a recording medium as usedwith magnetic disc recording systems, such as that shown in FIG. 1. Forsuch perpendicular recording the medium typically includes an underlayer 212 of a material having a high magnetic permeability. This underlayer 212 is then provided with an overlying coating 214 of magneticmaterial preferably having a high coercivity relative to the under layer212.

FIG. 2D illustrates the operative relationship between a perpendicularhead 218 and a recording medium. The recording medium illustrated inFIG. 2D includes both the high permeability under layer 212 and theoverlying coating 214 of magnetic material described with respect toFIG. 2C above. However, both of these layers 212 and 214 are shownapplied to a suitable substrate 216. Typically there is also anadditional layer (not shown) called an “exchange-break” layer or“interlayer” between layers 212 and 214.

In this structure, the magnetic lines of flux extending between thepoles of the perpendicular head 218 loop into and out of the overlyingcoating 214 of the recording medium with the high permeability underlayer 212 of the recording medium causing the lines of flux to passthrough the overlying coating 214 in a direction generally perpendicularto the surface of the medium to record information in the overlyingcoating 214 of magnetic material preferably having a high coercivityrelative to the under layer 212 in the form of magnetic impulses havingtheir axes of magnetization substantially perpendicular to the surfaceof the medium. The flux is channeled by the soft underlying coating 212back to the return layer (P1) of the head 218.

FIG. 2E illustrates a similar structure in which the substrate 216carries the layers 212 and 214 on each of its two opposed sides, withsuitable recording heads 218 positioned adjacent the outer surface ofthe magnetic coating 214 on each side of the medium, allowing forrecording on each side of the medium.

FIG. 3A is a cross-sectional view of a perpendicular magnetic head. InFIG. 3A, helical coils 310 and 312 are used to create magnetic flux inthe stitch pole 308, which then delivers that flux to the main pole 306.Coils 310 indicate coils extending out from the page, while coils 312indicate coils extending into the page. Stitch pole 308 may be recessedfrom the ABS 318. Insulation 316 surrounds the coils and may providesupport for some of the elements. The direction of the media travel, asindicated by the arrow to the right of the structure, moves the mediapast the lower return pole 314 first, then past the stitch pole 308,main pole 306, trailing shield 304 which may be connected to the wraparound shield (not shown), and finally past the upper return pole 302.Each of these components may have a portion in contact with the ABS 318.The ABS 318 is indicated across the right side of the structure.

Perpendicular writing is achieved by forcing flux through the stitchpole 308 into the main pole 306 and then to the surface of the diskpositioned towards the ABS 318.

FIG. 3B illustrates a piggyback magnetic head having similar features tothe head of FIG. 3A. Two shields 304, 314 flank the stitch pole 308 andmain pole 306. Also sensor shields 322, 324 are shown. The sensor 326 istypically positioned between the sensor shields 322, 324. The sensor 326may also have an overcoat 508 positioned thereabove (explained infurther detail below). The overcoat 508 may be positioned above themedia facing side of other portions of the head as well.

FIG. 4A is a schematic diagram of one embodiment which uses looped coils410, sometimes referred to as a pancake configuration, to provide fluxto the stitch pole 408. The stitch pole then provides this flux to themain pole 406. In this orientation, the lower return pole is optional.Insulation 416 surrounds the coils 410, and may provide support for thestitch pole 408 and main pole 406. The stitch pole may be recessed fromthe ABS 418. The direction of the media travel, as indicated by thearrow to the right of the structure, moves the media past the stitchpole 408, main pole 406, trailing shield 404 which may be connected tothe wrap around shield (not shown), and finally past the upper returnpole 402 (all of which may or may not have a portion in contact with theABS 418). The ABS 418 is indicated across the right side of thestructure. The trailing shield 404 may be in contact with the main pole406 in some embodiments.

FIG. 4B illustrates another type of piggyback magnetic head havingsimilar features to the head of FIG. 4A including a looped coil 410,which wraps around to form a pancake coil. Also, sensor shields 422, 424are shown. The sensor 426 is typically positioned between the sensorshields 422, 424. The sensor 426 may also have an overcoat 508positioned thereabove (explained in further detail below). The overcoat508 may be positioned above the media facing side of other portions ofthe head as well.

In FIGS. 3B and 4B, an optional heater is shown near the non-ABS side ofthe magnetic head. A heater (Heater) may also be included in themagnetic heads shown in FIGS. 3A and 4A. The position of this heater mayvary based on design parameters such as where the protrusion is desired,coefficients of thermal expansion of the surrounding layers, etc.

Various embodiments described and/or suggested herein may provide astructure and/or method for improving the film density, film height, andthermal resistance of an amorphous carbon overcoat, also referred toherein as a superhard amorphous carbon overcoat. Moreover, theembodiments described and/or suggested herein may preferably reduce thefilm thickness of the overcoats of the magnetic disk and the magnetichead. Furthermore, embodiments of the protective layers disclosed hereinprovide high thermal stability even in thermally-assisted magneticrecording systems, thereby enabling a higher recording density becauseof their higher reliability.

The superhard amorphous carbon overcoats according to variousembodiments may be formed by film deposition, while supplying anextremely small amount of hydrogen, thereby introducing an extremelysmall amount of hydrogen into the film. In contrast to conventionalmethods which essentially contain no hydrogen, a carbon film havinghydrogen content in a preferred range has been found to be ideal forimproving the reliability of the magnetic recording medium and/or themagnetic head because the film density is improved in some embodimentsby up to 20% or more, the film height is improved by at least 10%, andthe thermal resistance is improved.

FIG. 5 depicts a magnetic recording medium 500, in accordance with oneembodiment. As an option, the present magnetic recording medium 500 maybe implemented in conjunction with features from any other embodimentlisted herein, such as those described with reference to the other FIGS.Of course, however, such magnetic recording medium 500 and otherspresented herein may be used in various applications and/or inpermutations which may or may not be specifically described in theillustrative embodiments listed herein. Further, the magnetic recordingmedium 500 presented herein may be used in any desired environment.

Referring now to FIG. 5, the magnetic recording medium 500 may be amagnetic disc or any other suitable magnetic recording medium whichwould be apparent to one skilled in the art. As illustrated, themagnetic recording medium 500 preferably includes at least a groundlayer 504 e.g., a soft underlayer (SUL), a magnetic recording layer 506,and an overcoat 508 arranged above a non-magnetic substrate 502, but mayinclude any number of additional layers depending on the desiredembodiment.

In another embodiment, an overcoat may be an overcoat for a magnetichead, according to any approach presented herein, preferably having aplayback element (also referred to herein as a sensor). In a preferredapproach, the overcoat may be positioned above the media-facing side ofthe playback element (see 508 of FIGS. 3B and 4B). Moreover, theprotective layer may be embedded in, flush with and/or forming part of,offset from, protruding above, etc. the media-facing surface of themagnetic head. In one approach, the overcoat may be an overcoat for amagnetic head having an upper shield layer, a lower shield layer, and aplayback element provided between these layers. Moreover, the overcoatmay be an overcoat for a recording head having a lower magnetic pole, amain magnetic pole, a shield layer, and an auxiliary magnetic pole. Inanother approach, the overcoat may include an air-bearing surfaceovercoat, which may be formed on the surface of the playback element onthe side opposite the magnetic medium.

In further approaches, an overcoat may be provided on both the head andthe medium.

The following description provides additional detail about variousembodiments of overcoats, where such details may be generally applicableto any of the overcoats described herein, including those on a headand/or a medium.

The overcoat may be formed as an amorphous carbon film. Moreover, theamorphous carbon film may primarily be, e.g., greater than about 50 atom% (atomic percent) tetrahedral amorphous carbon, but is not limitedthereto. In a preferred approach, the superhard amorphous carbon filmmay have a high sp³ bond ratio. According to an illustrative example,the superhard amorphous carbon film may have a bonding ratio of sp³bonding with respect to sp² bonding (sp^(a)/(sp²+sp³)) of at least about0.5 (preferred), but could be higher or lower depending on the desiredembodiment.

With reference to FIG. 5, showing an overcoat 508 on a medium 500, anddiscussed here by way of example, the overcoat 508 may have at least afirst layer 510, second layer 512 and center layer 514. According tovarious approaches, the first, second and center layers may have thesame, similar, different, etc. compositions, or combinations thereof.Moreover, the first, center, and second layer may be discrete layers;may all be part of a continuously-formed overcoat layer where depositionconditions are varied to create a center layer having a differentcharacteristic than an adjacent one of the layers; and combinationsthereof.

In a particularly preferred approach, the first and second layers of theovercoat may have a composition different than the center layer of theovercoat.

As illustrated in FIG. 5, the center layer 514 of the overcoat may bedefined between the first layer 510 and the second layer 512 thereof.The first layer 510 may have a width w₁ of at least 0.5 nm in the filmthickness direction from a side of the center layer closest therecording layer in the film thickness direction. Furthermore, the secondlayer may have a width w₂ of at least 0.5 nm in the film thicknessdirection from a side of the center layer, opposite the first layer. Thethickness of the overcoat 508 may be in a range of between 1.25 nm and 5nm, but could be higher or lower.

The center layer of the overcoat may have a hydrogen content preferablyfrom about 0.1 atom % to about 0.6 atom %, more preferably from about0.2 atom % to 0.4 atom %, but may be higher or lower depending on thedesired embodiment. Moreover, the center layer may have a carbon contentof at least 85 atom %, more preferably 90 atom %, still more preferably95 atom %, but could be higher or lower depending on the desiredembodiment. In another approach, the average value of the hydrogencontent in the film in a given region having a carbon content of atleast 95 atom % in the overcoat may be specified from about 0.1 atom %to about 0.6 atom %, but could be higher or lower depending on thedesired embodiment.

According to various other approaches, the mass density of a magneticrecording medium and/or a magnetic head according to any of theembodiments described herein may be determined to be from about 3.3g/cm³ to about 3.6 g/cm³, by incorporating x-ray reflectometry.According to still other approaches, the mass density of the overcoatmay be from about 3.3 g/cm³ to about 3.6 g/cm³, more preferably fromabout 3.53 g/cm³ to about 3.6 g/cm³ as determined by incorporating x-rayreflectometry, but could be higher or lower depending on the desiredembodiment.

FIG. 6 depicts a method 600 for forming an overcoat, in accordance withone embodiment. As an option, the present method 600 may be implementedin conjunction with features from any other embodiment listed herein,such as those described with reference to the other FIGS. Of course,however, such method 600 and others presented herein may be used invarious applications and/or in permutations which may or may not bespecifically described in the illustrative embodiments listed herein.Further, the method 600 presented herein may be used in any desiredenvironment.

Referring now to FIG. 6, the method 600 includes forming an overcoatabove at least one of a magnetic layer of a magnetic medium and amedia-facing side of the playback element, the overcoat characterized inthat the overcoat is an amorphous carbon film having a ratio of sp³bonding with respect to sp² bonding (sp³/(sp²+sp³)) of at least 0.5, andhydrogen content in the film in a center layer in a film thicknessdirection of the overcoat is in a range of from 0.1 atom % to 0.6 atom%. See operation 602.

Referring to operation 604, the hydrogen content of the overcoat isadjusted to be in the preferred range by adjusting a flow of hydrogengas into a film deposition chamber during deposition of the overcoat,and by adjusting a hydrogen gas pressure in the film deposition chamber.In a preferred approach, when the overcoats are formed, the hydrogen gaspressure in the film deposition chamber may be specified to be in therange from about 3.0×10⁻² Pa to about 6.0×10⁻² Pa, more preferably, inthe range from about 4.5×10⁻² Pa to about 5.5×10⁻² Pa, but could behigher or lower depending on the desired embodiment.

According to an illustrative example, which is in no way intended tolimit the invention, the hydrogen content in the film may be measured byhigh-resolution elastic recoil detection analysis (HR-ERDA), a highlysensitive recoil particle detection method for hydrogen analysis, whichtargets hydrogen from the elastic recoil detection. Correspondingmanufacturing methods for forming the overcoats for the magneticrecording medium and the magnetic head may adjust the hydrogen contentin the overcoat to a preferred hydrogen-content range as describedabove. According to one approach, the manufacturing methods may adjustthe hydrogen content by adjusting the flow of hydrogen gas supplied fromthe outside into the film deposition chamber during film deposition, andadjusting the hydrogen gas pressure in the film deposition chamber.

According to various approaches, the manufacturing method of thesuperhard amorphous carbon film is not particularly limited and may be amethod capable of adjusting the hydrogen content within a range ofextremely small amounts, preferably within the ranges described above.According to one approach, this may be possible by including anextremely small amount of hydrogen in the carbon film by supplying asmall amount of hydrogen gas into the film deposition chamber duringfilm deposition. Moreover, the film may be formed by various methods,including, but not limited to a filtered cathodic vacuum arc (FCVA)method, which may be used form a superhard amorphous carbon film havinga low number of particles by including a magnetic field filter.

Without wishing to limit the scope of the invention, illustrativeworking examples are explained below, which correspond to thecharacteristics of an about 2.5 nm thick superhard amorphous carbon filmthat includes an small amount (e.g., from about 0.1 atom % to about 0.6atom %) of hydrogen in the film. As described above, the small about ofhydrogen in the film may be achieved by supplying an extremely smallamount of hydrogen gas into a film deposition chamber during filmdeposition, and the manufacturing method thereof.

According to the first working example, which again is in no wayintended to limit the invention, a superhard amorphous carbon filmhaving a film thickness of about 2.5 nm was formed on a Simonocrystalline substrate. The amount of hydrogen gas supplied to theinterior of a film deposition chamber was varied, and the film densityand film hardness were evaluated with respect to the hydrogen content inthe film. According to various approaches, the substrate may include achemically hardened glass substrate, a substrate with the surfacepolished after plating e.g., Ni—P on an aluminum alloy substrate, etc.Moreover, the shape of the substrate can be freely selected, dependingon the desired embodiment.

With continued reference to the first working example the film densitywas measured by X-ray reflectometry. The resulting measurements areshown in the graph of FIG. 7, where the horizontal axis represents thehydrogen content in the film and the vertical axis represents the filmdensity. According to this results depicted in FIG. 7, the film densityimproves in the region where the hydrogen content in the film is fromabout 0.1 atom % to about 0.6 atom %. Furthermore, the film densityimproves by approximately 20% in region 702 where the hydrogen contentis from about 0.2 atom % to about 0.4 atom %, compared to a conventionalfilm of region 701 formed without supplying hydrogen.

Referring now to FIG. 8 the measurements of the film hardness, measuredby incorporating a nanoindenter method, are shown. In the graph depictedin FIG. 8, the horizontal axis represents the hydrogen content in thefilm and the vertical axis represents the film hardness. According tothe result shown in the graph, in a region where the hydrogen content inthe film is from about 0.1 atom % to about 0.6 atom %, the film hardnessimproves similarly to that of the film density depicted in FIG. 7.Furthermore, the film hardness improves by approximately 10% in region704 where the hydrogen content is from about 0.2 atom % to about 0.4atom %, compared to that of a conventional film 703 formed withoutsupplying hydrogen.

According to a second working example, a similar film structure as usedin the first working example was used; however, three samples havingdifferent hydrogen content in the film (0 atom %, 0.3 atom %, 2.5 atom%) were fabricated. The samples were heated by a hot plate set to thetemperature of 500° C., and the residual film thickness of the carbonfilm was measured with respect to the heating time.

FIG. 9 shows the measurements of the changes in the film thickness,wherein spectroscopic ellipsometry was used to measure the filmthickness. Moreover, high-resolution elastic recoil particle detectionfor analyzing hydrogen (HR-ERDA) was included to measure the hydrogencontent of the working example. With reference to the graph of FIG. 9,the horizontal axis represents the heating time and the vertical axisrepresents the film thickness. According to the results shown in FIG. 9,for samples having a hydrogen content in the film of 0 atom % 705 and2.5 atom % 706, for the heating times of 100 seconds and 450 secondsrespectively, the film thickness is seen to decrease by approximately80%. In contrast, for the heating time of 450 seconds, a sample having0.3 atom % 707 has a decrease in the film thickness of less than 10% andstrong thermal resistance.

From the above results, it is apparent that the carbon film in a regionhaving hydrogen content in the film from about 0.1 atom % to about 0.6atom % has strong thermal resistance compared to carbon film havinghydrogen content outside of the above range. Therefore, according to apreferred approach, this film may be the overcoat for the magneticrecording medium and the magnetic head for energy-assisted magneticrecording having heat generated on the magnetic recording medium and themagnetic head. For example, this film may be the overcoat in thermallyassisted magnetic recording that provides thermal energy to the magneticrecording medium from the magnetic head during recording to facilitatewriting or in microwave assisted magnetic recording that applies ahigh-frequency AC magnetic field to facilitate writing.

According to a third working example, which again is in no way intendedto limit the invention, a superhard amorphous carbon film having a filmthickness of about 2.5 nm was formed on a Si monocrystalline substrateand on a glass substrate with a deposited magnetic recording layer toevaluate the hydrogen concentration in the carbon film. According to thegraph depicted in FIG. 10, three superhard amorphous carbon films 708,709, 710 having different amounts of hydrogen gas supplied to theinterior of the film deposition chamber when being formed, and a film711 formed by a CVD method were evaluated.

FIG. 10 shows the measurements of the hydrogen content in the carbonfilm on a Si substrate wherein the horizontal axis represents the depthfrom the top surface of the overcoat, and the vertical axis representsthe hydrogen content. Moreover, the depth was measured byhigh-resolution elastic recoil detection analysis for hydrogen analysis(HR-ERDA) and by high-resolution Rutherford backscattering spectrometry(HRRBS).

With continued reference to the graph of FIG. 10, in the region at adepth of 0.5 nm from the top surface, the components in the air areabsorbed by the top surface when extracted from the vacuum depositionchamber. In addition, in the 0.5 nm region on the Si substrate side, byforming a mixed layer of the carbon film and the top surface layer ofthe Si substrate, there is a distribution of hydrogen content in thedepth direction. In a region excluding the 0.5 nm layer on the topsurface of the overcoat thickness and the 0.5 nm layer on the substrateside, hydrogen content in the film is nearly constant.

Referring now to FIGS. 11A-11B, the measurements of the hydrogen contentin the carbon film on the glass substrate formed with a depositedmagnetic recording layer are shown in the graphs. The horizontal axis ofthe graphs represents the depth from the top surface of the overcoatwherein the vertical axis represents the element concentration.Moreover, three superhard amorphous carbon films 712, 713, 714 havingdifferent amounts of hydrogen gas supplied to the interior of the filmdeposition chamber when being formed; film 714 being formed by a CVDmethod were evaluated.

Similar to the evaluation results of the Si substrate depicted in FIG.10, the hydrogen content has a distribution in the depth direction ofthe film thickness. In the region excluding the 0.5 nm layer on the topsurface side of the overcoat thickness and the 0.5 nm layer on thesubstrate side, the hydrogen content in the film is nearly a constantvalue. When the results of the first and second working examples arecombined, in the region excluding the 0.5 nm layer on the top surfaceside of the overcoat thickness and the 0.5 nm layer on the substrateside, the film characteristic is determined by the average value of thehydrogen content in the film. In addition, the hydrogen content in thefilm is monitored and can be appropriately controlled to be within thetolerance (0.1 atom % to 0.6 atom %).

According to one embodiment, the overcoat is suitable for controlling anextremely small hydrogen concentration when composed of superhardamorphous carbon film using a physical vapor deposition means utilizingcarbon ions. According to various approaches, the superhard amorphouscarbon film may be formed by incorporating ion beam vapor depositionmethods, low gas pressure-high current sputtering methods, etc. or othermethods which would be apparent to one skilled in the art upon readingthe present description.

In an illustrative embodiment, which is in no way intended to limit theinvention, a vapor deposition device as shown in FIG. 12 may be used toform overcoats using an arc discharge. As depicted in FIG. 12, a plasmabeam 716 formed by an arc discharge unit 715 is used as an ion source(explained in further detail below). A plasma beam 716 is generated froman arc discharge unit 715 arranged to enable the processing of bothsurfaces of the magnetic disk substrate 717 being processed.Specifically, a voltage, from a voltage source 727, is applied between acathode 718 and an anode 719 composed of carbon to generate an arcdischarge 720 in a high vacuum atmosphere.

As a result, the cathode 718 enters an extremely high temperature statesimilar to arc welding and plasma (e.g., a state generating positivelycharged carbon ions 721 and electrons 722) is generated from the cathodesurface. In addition, the arc current in the cathode 718 flows in atapproximately 50 amperes and generates an arc discharge with an arcvoltage of approximately −20 volts. The generated carbon ions 721 andelectrons 722 pass through a curved magnetic field duct 723 for removingthe droplets generated during the arc discharge and for transporting theplasma, are introduced into a film deposition chamber 725 holding themagnetic disk substrate 717 being processed, and are uniformly radiatedon the magnetic disk substrate 717 being processed by a scanningelectromagnet 726. Moreover, the magnetic disk substrate 717 beingprocessed is electrically floated.

The incident carbon ions are applied at an energy of approximately 50eV, and the plasma beam 716 irradiates carbon ions 721 and electrons 722for overall neutrality. Because only the cathode 718 composed of carbonis used, a superhard amorphous carbon film containing almost no hydrogenis formed. In this working example, the magnetic disk substrate 717being processed was electrically floated, but is not restricted to this,and is not a problem in a vapor deposition method that applies asubstrate bias.

With continued reference to FIG. 12, when the plasma beam 716 irradiatesan unprocessed magnetic disk substrate 717, hydrogen gas is suppliedfrom the outside into the film deposition chamber 725. In this case, byusing a mass flow controller 729 to adjust the supplied amount ofhydrogen gas, the hydrogen pressure in the film deposition chamber 725is held at the specified pressure, and the hydrogen content in thesuperhard amorphous carbon film can be adjusted to the desired value.

According to a preferred approach, the hydrogen gas pressure in the filmdeposition chamber 725 may be in the range from about 3.0×10⁻² Pa toabout 6.0×10⁻² Pa, but could be higher or lower depending on the desiredembodiment. The supplied hydrogen gas is excited by the plasma beam 716to generate hydrogen radicals, wherein the radicals bond to danglingbonds of carbon caused by disorder in the structure. Moreover, this maybe caused by the radicals being taken into the superhard amorphouscarbon film. As a result the film density, film hardness, and thermalresistance may be high, thereby achieving a more chemically stablestate. Although the hydrogen gas was supplied into the film depositionchamber 725 for the illustrative embodiment depicted in FIG. 12,according to another approach, the gas may be supplied to a locationother than the film deposition chamber 725, such as where the hydrogengas can be excited by the plasma beam 716.

It should be noted that methodology presented herein for at least someof the various embodiments may be implemented, in whole or in part, incomputer hardware, software, by hand, using specialty equipment, etc.and combinations thereof. In one illustrative approach, a magneticrecording device may be included in a magnetic recording medium and/ormagnetic head according to any of the embodiments described and/orsuggested herein.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A magnetic recording medium, comprising: at leasta ground layer above a non-magnetic substrate; a magnetic recordinglayer above the ground layer; and an overcoat above the magneticrecording layer, the overcoat characterized in that said overcoat is anamorphous carbon film having a ratio of sp³ bonding with respect to sp²bonding (sp³ t(sp²+sp³)) of at least 0.5, and hydrogen content in theovercoat in a center layer thereof in a film thickness direction of saidovercoat is from 0.1 atom % to 0.6 atom %.
 2. The magnetic recordingmedium as recited in claim 1, wherein the center layer of the overcoatis defined between a first layer and a second layer of the overcoat, thefirst layer extending at least 0.5 nm in the film thickness directionfrom a side thereof closest the recording layer in the film thicknessdirection, and a second layer extending at least 0.5 nm in the filmthickness direction from a side thereof opposite the first layer.
 3. Themagnetic recording medium as recited in claim 2, wherein the first andsecond layers have a composition different than the center layer.
 4. Themagnetic recording medium as recited in claim 1, wherein the amorphouscarbon is primarily tetrahedral amorphous carbon.
 5. The magneticrecording medium as recited in claim 1, wherein the center layer has acarbon content of at least 95 atom %.
 6. The magnetic recording mediumas recited in claim 1, wherein a mass density of the overcoat is in arange of 3.3 g/cm³ to 3.6 g/cm³ as determined by x-ray reflectometry. 7.The magnetic recording medium as recited in claim 1, wherein a massdensity of the overcoat is in a range of 3.5 g/cm³ to 3.6 g/cm³ asdetermined by x-ray reflectometry.
 8. The magnetic recording medium asrecited in claim 1, wherein hydrogen content in the overcoat in a centerlayer thereof in a film thickness direction of said overcoat is from 0.2atom % to 0.4 atom %.
 9. A magnetic data storage system, comprising: atleast one magnetic head; a magnetic medium as recited in claim 1; adrive mechanism for passing the magnetic medium over the at least onemagnetic head; and a controller electrically coupled to the at least onemagnetic head for controlling operation of the at least one magnetichead.
 10. A magnetic head, comprising: a playback element; and anovercoat above a media-facing side of the playback element, the overcoatcharacterized in that said overcoat is an amorphous carbon film having aratio of sp³ bonding with respect to sp² bonding (sp³/(sp²+sp³)) of atleast 0.5, and hydrogen content in the film in a center layer in a filmthickness direction of said overcoat is from 0.1 atom % to 0.6 atom %.11. The magnetic head as recited in claim 10, wherein the center layerof the overcoat is defined between a first layer and a second layer ofthe overcoat, the extending at least 0.5 nm in the film thicknessdirection from a side thereof closest the playback element in the filmthickness direction, and a second layer extending at least 0.5 nm in thefilm thickness direction from a side thereof opposite the first side.12. The magnetic head as recited in claim 11, wherein the first andsecond layers have a composition different than the center layer. 13.The magnetic head as recited in claim 10, wherein the amorphous carbonis primarily tetrahedral amorphous carbon.
 14. The magnetic head asrecited in claim 10, wherein the center layer has a carbon content of atleast 95 atom %.
 15. The magnetic head as recited in claim 10, wherein amass density of the overcoat is in a range of 3.3 g/cm³ to 3.6 g/cm³ asdetermined by x-ray reflectometry.
 16. The magnetic head as recited inclaim 10, wherein a mass density of the overcoat is in a range of 3.5g/cm³ to 3.6 g/cm³ as determined by x-ray reflectometry.
 17. Themagnetic head as recited in claim 10, wherein hydrogen content in theovercoat in a center layer thereof in a film thickness direction of saidovercoat is from 0.2 atom % to 0.4 atom %.
 18. A magnetic data storagesystem, comprising: at least one magnetic head as recited in claim 10; amagnetic medium; a drive mechanism for passing the magnetic medium overthe at least one magnetic head; and a controller electrically coupled tothe at least one magnetic head for controlling operation of the at leastone magnetic head.
 19. A method, comprising: forming an overcoat aboveat least one of a magnetic layer of a magnetic medium and a media-facingside of the playback element, the overcoat characterized in that saidovercoat is an amorphous carbon film having a ratio of sp³ bonding withrespect to sp² (sp³/(sp²+sp³)) bonding of at least 0.5, and hydrogencontent in the film in a center layer in a film thickness direction ofsaid overcoat is in a range of from 0.1 atom % to 0.6 atom %, whereinthe hydrogen content of said overcoat is adjusted to be in said range byadjusting a flow of hydrogen gas into a film deposition chamber duringdeposition of the overcoat, and by adjusting a hydrogen gas pressure insaid film deposition chamber.
 20. The method as recited in claim 19,wherein the hydrogen gas pressure in the film deposition chamber whensaid overcoat is formed is in a range from 3.0×10⁻² Pa to 6.0×10⁻² Pa.21. The method as recited in claim 19, wherein the hydrogen gas pressurein the film deposition chamber when said overcoat is formed is in arange from 4.5×10⁻² Pa to 5.5×10⁻² Pa.